For example, when blood ejected from the heart is pumped through a blood vessel, the inside diameter of the blood vessel is enlarged by a pressure where a high-pressure region propagates. The development of a pulse wave velocity measuring apparatus is in progress that measures changes inside a blood vessel (artery) by measuring a propagation velocity at which the enlarged portion of the diameter of the blood vessel propagates (also referred to as pulse wave velocity). (See, for example, Patent Document 1.)
According to the pulse wave velocity measuring apparatus, when a time difference is calculated between a periodically occurring predetermined portion of an electrocardiographic lead waveform detected with an electrocardiographic lead unit and a periodically occurring predetermined portion of a pulse wave detected with a pressure pulse wave sensor, the propagation velocity of a pulse wave in an artery is calculated based on the time difference. The propagation velocity is calculated based on a distance including propagation in the aorta connected to the heart. Therefore, in the pulse wave velocity measuring apparatus, the accuracy of the pulse wave velocity increases as the propagation time, that is, the time difference, increases because of a lower pulse wave velocity in the artery due to a long propagation distance and a large aorta diameter.
Further, there is a pulse wave sensor that measures a pulse wave from the waveform of a signal at the time of receiving light that has passed through a blood vessel after exposing a measurement region of a subject to light. (See, for example, Patent Document 2.)